The dynamic performance of a voltage-feedback amplifier (i.e., its ability to accurately amplify time-varying signals) is limited by its gain-bandwidth product (“GBW”) and slew rate. Because the GBW of a voltage amplifier is constant, the closed-loop bandwidth is inversely proportional to its gain; if a given amplifier is configured for a high gain, for example, its bandwidth correspondingly drops (sometimes dramatically). This drop in bandwidth may degrade the amplifier's performance, especially with high-frequency inputs. Some amplifiers (such as general-purpose instrumentation amplifiers) include an input/output port (e.g., pins on a chip package) to which a customizable gain-setting resistor (“RG”) may be connected; other amplifiers include a control port for digitally programming an internal RG value. A user may therefore select a desired gain value by varying the size of RG but, in doing so, deleteriously change the amplifier's bandwidth. FIG. 1 illustrates an exemplary three operational-amplifier (“op-amp”) instrumentation amplifier 100 that includes first-level op-amps 102 (divided into first-stage A1 and second-stage A2 amplifiers) and a second-level op-amp 104.
If the gain is set to a high value, the resulting low bandwidth of the amplifier 100 may be increased by configuring other components in the circuit. For example, part of the amplifier's compensation capacitance 106 may be switched out (i.e., electrically disconnected from the circuit), thereby improving the high-frequency performance of the circuit. This adjustment, however, requires additional input/output ports for the control signals necessary to change the compensation capacitance 106; in the simplest case, one pin may be used to switch part of the capacitance 106 in or out, but more pins are required for finer-grained control. Many amplifiers, such as commercial general-purpose resistor-programmable instrumentation amplifiers, cannot provide these additional ports because they would increase the cost of the amplifier, the complexity of the control circuitry, and/or the size of the amplifier package. A current-feedback amplifier may be used for high-speed operation, because its dynamic performance is not limited by GBW and slew rate, but these amplifiers have lower DC gain and are thus not suitable for high-precision applications. A need therefore exists for a way of boosting the bandwidth of a voltage-feedback amplifier at high gains without requiring additional input/output ports.